In general, a tub is installed in the interior space of a cabinet which constitutes the external appearance of a washing machine. The tub is supported by a damper connected on the upper side of a tub, and stores the washing water in the interior. And, a laundry tray is installed rotatably in the interior of the tub. Particularly, as several opening are formed on the lower part and the flank of the laundry tray, the washing water stored in the tub flows between the laundry tray and the tub, and so the impurities are removed.
In another aspect, a heater which make the washing water hot as heating is installed on the bottom of the tub. Therefore, it isn't necessary to connect with a hot water dripping tap separately, because the washing water is heated as a certain temperature as a heater is operated, even if the cold water is flown into the interior of the tub in the winter.
The conventional technique on a tub having a heater which operates with the same as the above mentioned functions is recorded particularly on the official report of the Republic of Korean special permission licenses “10-2003-0055973.”
However, generally a tub is an injection molded plastic that the strength is lower than a heater or a voltage. Therefore, according to the stress which occurred on the interior of the tub like the above-mentioned is continuously given, a crack is occurred on a part of the tub where the heater is united. In that case, the disadvantages like the product reliance is decreased greatly, etc as the washing water is leaked through the crack, etc are occurred.